Energy costs represent a significant portion of many household budgets. It is generally accepted that it is desirable to reduce the amount of energy being consumed in a household in order to reduce the household's total expenditure on energy costs. In many cases, a significant portion of these energy costs are directly attributable to energy used to heat water for a domestic hot water installation.
Domestic hot water installations comprise a hot water cylinder in which hot water is stored for subsequent use in the household, e.g. for baths, showers and also for supply to sinks and kitchen appliances. Typically, the hot water cylinder has a capacity for between 200 and 300 litres of water. More often than not, this far exceeds the amount of hot water required at a given point in time. For example, a 5 minute shower is estimated to require approximately 33 litres of hot water from the hot water cylinder. If the entire tank is heated for the purpose of an individual having a shower, which is not an entirely uncommon occurrence, then a significant amount of energy has been wasted heating the remaining water in the tank unnecessarily.
Various solutions have been proposed to address this problem. One common solution is to provide a timer clock on the immersion heater so that the immersion is programmed to operate for a predetermined period of time. Although this goes some way to addressing the problem of the entire hot water cylinder being heated unnecessarily, it is still not entirely satisfactory as it is a crude way of determining how much hot water will be available for use in the household. The homeowner will effectively have to guess the length of time that it is necessary to power the immersion and will use trial and error in order to ensure that a sufficient amount of hot water will be available for use in the household. This often results in excess hot water being made available and a waste in energy. Furthermore, these systems are not suitable for domestic hot water installations that operate using an external water heating circuit such as a boiler or an external electrical water heater rather than an immersion heater.
Another solution that has been proposed that is more suited to hot water installations that are not immersion based but instead are boiler based, is to provide a large number of temperature sensors connected to the exterior of a hot water cylinder. The temperature sensors are connected at discrete locations spaced apart from each other and are used to measure the temperature at each of the discrete locations. In this way, it is possible to measure with a reasonable degree of accuracy the volume of hot water in the hot water cylinder at any given time. However, the sensors are relatively expensive and increase the overall cost of the cylinder significantly. This has resulted in a cylinder that is not price competitive and unpopular in the market place.
It is an object of the present invention to provide a hot water installation and a method of operating a hot water installation that overcomes at least some of these problems and offers a useful choice to the consumer.